The hydrophilicity of human prostatic and lysosomal acid phophatases were analyzed and the relative antigenicity (capacity to bind antibodies raised against the intact prostatic acid phosphatase) of the selected peptides was evaluated in a competitive assay. Both prostatic and lysosomal acid phosphatases were shown to possess similar antigenic structure on both terminal regions, along with more similarity on NH2-terminal peptide than COOH-terminal site. At least one additional antigenic site is present at the internal region of prostatic acid phosphatase, since the mixture of both amino- and carboxyl-terminal peptides exhibited only 70% inhibition. The collaborative protein chemistry laboratory with UNC has already provided lots of research services on protein microsequencing and peptide synthesis to other scientists at the NIEHS.